Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
The term "battery" is generally used to describe a single unit comprising one or more electric current producing cells. The electric current is produced directly by chemical reactions which occur within the battery. The terms "battery," "battery cells," "electric current producing cells," and "cells" are used interchangeably herein.
Current limiting or overcurrent protection devices of various designs which function by limiting current flow have been used for preventing overcurrent conditions from damaging the battery or cell and potentially leading to an unsafe condition. A typical current limiting protection device is a PTC device, where PTC is an abbreviation for "Positive Temperature Coefficient" and refers to the property of the device such that the electrical resistance of the device increases sharply when the PTC device is heated. When utilized for internal temperature protection in batteries, PTC devices function by heating up rapidly when the flow of current in the battery is at a high level and thereby greatly increasing the electrical resistance of the PTC device, which then suppresses or limits the high current flow. Without the PTC device to limit the current, a high current flow in the battery, such as that caused by a short circuit in the battery, would increase the temperature of the battery and may lead to an unsafe condition (e.g., venting, explosion).
Materials and compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Examples of useful materials compositions and electrical applications are those described in U.S. Pat. No. 3,861,029 to Smith-Johannsen et al.; U.S. Pat. No. 3,823,217 to Kampe; U.S. Pat. No. 4,177,376 to Horsma et al., U.S. Pat. No. 4,188,276 to Lyons et al.; U.S. Pat. No. 4,237,441 to van Konynenburg et al.; U.S. Pat. No. 4,238,812 to Middleman et al.; U.S. Pat. No. 4,255,698 to Simon; U.S. Pat. No. 4,304,987 to van Konynenburg; U.S. Pat. No. 4,329,726 to Middleman et al.; U.S. Pat. No. 4,330,703 to Horsma et al.; U.S. Pat. No. 4,388,607 to Toy et al.; U.S. Pat. No. 4,426,633 to Taylor; U.S. Pat. No. 4,514,620 to Cheng et al.; U.S. Pat. No. 4,534,889 to van Konynenburg et al.; U.S. Pat. No. 4,543,474 to Horsma et al.; U.S. Pat. No. 4,560,498 to Horsma et al.; U.S. Pat. No. 4,591,700 to Sopory; U.S. Pat. No. 4,603,165 to McDonald et al.; U.S. Pat. No. 4,654,511 to Horsma et al.; U.S. Pat. No. 4,922,242 to Parker; U.S. Pat. No. 5,602,520 to Baiatu et al.; and U.S. Pat. No. 5,609,972 to Kaschmitter et al. A typical PTC device is a POLYSWITCH material (a trademark for PTC devices available from Raychem Corporation, Menlo Park, Calif., and as described in the Current Protection Data Book for POLYSWITCH.TM. Resettable Fuses (February 1997) available from Raychem Corporation, Menlo Park, Calif.).
These overcurrent devices generally use a stacked array of circular stampings consisting of the current limiting protective device, insulators, contacts, support cups, and end caps which are situated at the top of the cells, typically on a crimped bead, and held in place by a crimped-over edge of the can of the cell, and are typically referred to as header assemblies. For example, U.S. Pat. No. 4,971,867 to Watanabe et al. describes a cylindrical organic electrolyte battery with a conventional installation of the PTC device at the top of the cell, and a different installation with the PTC device attached to the bottom of the battery case through a metal plate so that the upper opening of the battery case can be tightly sealed.
There are a variety of crimped seal designs for use in batteries. For example, U.S. Pat. No. 5,422,201 to Georgopoulos describes a seal body and a compression means for a cell with a crimped seal design. U.S. Pat. No. 4,053,687 to Coibion et al. describes an arrangement for the conductive borders of the electrodes for a cell with a crimped seal design. Many crimped seal designs for use in batteries utilize a beaded seal surface on the inside opening of the battery can to locate and position the header prior to crimping. All of the header parts, whether they include PTC current limiting devices or not, are typically inserted and stacked up on this internal beaded surface prior to crimping. Usually several washers, a plastic seal ring, other devices including PTC devices and safety vents, and the positive end cap are inserted into the cell through the top. A crimp is then rolled over onto the stack of devices and plastic seal ring. The formed metal bead of the inside beaded seal surface and the rolled over crimp clamp the stack of parts together. Sealing is obtained by the plastic seal ring being in compression between the rolled over crimp and the beaded seal surface on the inside of the can. The header then becomes the lid of the can after the crimping is performed. FIG. 1 illustrates a typical header assembly of a crimped seal design. The battery comprises a cell can, 101, in which is contained a battery stack, 102, comprising the negative and positive electrodes separated by a separator insulation layer. A tab, 103, connects one of the electrodes to the header assembly, 104. The header assembly comprises sealing plates, 105 and 106, a metal plate, 107, a PTC plate, 108, an end cap, 109, and insulating members, 110 and 111. The header assembly is situated on a crimp bead, 112, and held in place by a crimped-over edge of the can, 113.
The addition of a part, such as the PTC current limiting device, to the header is usually done by the addition or modification of the stack of parts that make up the header assembly. For example, U.S. Pat. Nos. 4,966,822 and 5,008,161 to Johnston describe batteries compatible with a crimped seal design and comprising a thermal disconnect or current limiting assembly between the end cap and a plate to which the terminal pin is attached. U.S. Pat. No. 4,855,195 to Georgopoulos et al. describes a current collector with a PTC device for use with cells with a crimped seal design.
In contrast, glass-to-metal, plastic-to-metal, and related seals for batteries do not commonly employ a PTC current limiting protection device. Glass-to-metal, plastic-to-metal, and similar types of seals for electrochemical cell terminals, particularly for sealing thin terminal pins, are difficult to achieve with complete hermetic sealing, reliable electrical contact, permanent isolation of the positive and negative terminals of the cell, and resistance to fracturing or breaking under conditions of rough usage or cell expansion by reason of shorting. For example, U.S. Pat. No. 4,158,721 to Decker et al. describes the use of a special tack shaped terminal pin of greater contact area to make more reliable glass-to-metal seals for electrochemical cells. U.S. Pat. No. 4,707,424 to Bowsky et al. describes the use of a terminal pin and an eyelet with an aperture for glass-to-metal seals of electrochemical cells. U.S. Pat. No. 4,053,692 to Dey describes a hermetic seal comprising a glass ring sealed to a metal. Also, for example, U.S. Pat. No. 4,358,514 to Garoutte et al. describes a hermetic glass-to-metal seal fabricated using a bonding temperature of at least 1800.degree. F. (982.2.degree. C.). U.S. Pat. No. 4,445,920 to Smith describes a glass-to-metal seal made using a bonding temperature of 1050.degree. C. U.S. Pat. No. 4,792,503 to Eppley describes a hermetic glass-to-metal seal of a stainless steel header to a stainless steel terminal pin.
In order to also incorporate current limiting protective devices, glass-to-metal or similarly sealed cells require a different type of design for the header assembly than are utilized with crimp sealed cells. No shorting of the cell can be allowed even with a failure in the insulating cover of the cell. One requirement for the mechanical design is the attachment of the PTC current limiting device to a current feedthrough pin, typically of small diameter (e.g., 0.062 inches, .about.1.6 mm). One limitation on the attachment method is the range of temperatures allowed during the metal-to-metal attachment. Secondly, the connection has to be as electrically conductive as the base metals. Thirdly, the attachment process has to be very repeatable and easily adapted to automation.
The stacked and crimped design for header assemblies incorporating the overcurrent protection device typically requires a significant amount of space in the cell and has reliability limitations for use in batteries at temperatures and humidities at the upper end of the range of normal operating conditions. It would be advantageous to reduce the space required for the header assembly incorporating the overcurrent protection device and to provide a header assembly with a design and method of sealing with increased reliability at the higher temperatures and humidities, which is not offered by the stacked and crimped design. By reducing the space required for the overcurrent protection device and seal design, a battery containing the overcurrent protection header can contain more electroactive materials, thereby yielding a battery with increased energy density.
To increase the reliability at higher temperatures and humidities while also providing an overcurrent protection device utilizing a reduced space, header assemblies with more reliable non-crimped seal designs, such as cells utilizing glass-to-metal, plastic-to-metal, and other related types of terminal pin contact feedthroughs integrated with a current limiting protective device, would be advantageous, but such types of header assemblies for use in batteries have not heretofore been reported.